European Patent 0 074 690, POSTMA, discloses an electrodeless gas discharge lamp having a vacuum impervious sealed glass envelope filled with metal vapor and a rare gas, the lamp envelope enclosing a rod shaped core of magnetic material in which a high frequency magnetic field may be induced by a source of electric current whereby an electric field may be generated within the envelope of the lamp.
Furthermore, U.S. Pat. No. 4,959,592, ANDERSON & ROBERTS, and its corresponding German Offenlegungsschrift DE-OS 39 18 839 describe a high intensity electrodeless discharge lamp with an envelope located within the cavity of an excitation coil and with a discharge plasma driven by the excitation coil, high voltage pulses being coupled between a pair of starting electrodes positioned outside of the envelope for inducing the material within the lamp envelope to create a spark channel in which the plasma may be formed in response to the field provided by the excitation coil.
In electrodeless high pressure gas discharge lamps the stability or continuity of the discharge, and the spectrum consisting solely of lines or continuum of superimposed lines may pose problems even though their radiant density and radiant flux may attain relatively high values. On the other hand, electrodeless low pressure gas discharge lamps are of sufficient stability, yet their radiant density and radiant flux are of relatively low value.
Moreover, German Offenlegungsschrift DE-OS 39 08 553, THOMAS et al., discloses a gas discharge lamp filled with deuterium or hydrogen and having a housing positioned within the lamp envelope, which in the discharge path between cathode and anode is provided with an aperture member made of a material of a high melting point, the arc discharge generated between the electrodes being constricted by means of the aperture opening.